This invention relates to voltage regulators for supplying voltage to a load circuit, and particularly to protection of the load from the effects of overvoltage under fault conditions.
In order to avoid the weight and cost of a line isolation transformer, television receivers may be supplied with power directly from the AC power line through a rectifier and filter. The filtered direct voltage will vary in proportion to the variations in the AC power line voltage, which may be undesirable. Also, the value of the filtered direct voltage will be approximately the peak value of the alternating-current input, which may be greater or less than the desired value.
It is possible to produce a regulated output voltage of lesser magnitude than the raw DC input by use of a series-pass regulator circuit, but this has the disadvantage of substantial power dissipation when the load current and the difference between the raw voltage and the regulated voltage are large. It is known from U.S. Pat. No. 3,881,135 issued Apr. 29, 1975 in the name of Wolfgang Dietz to produce a boosted regulated voltage in a television receiver by coupling a transformer winding and controlled rectifier in series with the raw DC input. The transformer winding is driven by the horizontal deflection circuit, and the resulting alternating voltage is controllably rectified and filtered to produce the regulated output voltage. In the Dietz arrangement, the load is protected against excessive regulated voltage by a clamp arrangement including a zener diode and an SCR which clamps the boosted regulated output voltage to the raw input voltage when the difference between the two exceeds the zener voltage.
In order to reduce voltage stresses on horizontal output transistors, it may be desirable to have the regulated output voltage less than the raw DC voltage. This is accomplished by a de-boost arrangement, by which the raw voltage is reduced to a lower regulated voltage by means of a transformer winding, controlled rectifier and capacitor. It is desirable to provide overvoltage protection of the de-boost regulator to prevent damage to the horizontal output transistor in case of overvoltage faults.